KMS Linux (very basic question)

I have seen KMS being mentioned as part of an optimal Linux setup and was wondering if anyone could help me understand it.

If I had a full OS installed such as Ubuntu, Fedora etc. and enable KMS am I right in thinking it only has an effect outside of the Desktop Manager?

I.E. in terms of RetroArch I only get the benefits if I boot directly into RetroArch without loading the Desktop Manager.

You don’t have to boot directly to it. You can drop down to it by pressing ctrl+alt+F1 or otherwise stopping your desktop manager. But, otherwise, yeah, it only works from console.

Thanks for the clarification.